SiO2 (silicon dioxide) films having a dielectric constant of 3.9 to 4.0 have long been used as the insulating films such as interlayer insulting films within semiconductor devices, but in recent years, because miniaturization has progressed significantly and higher speeds and higher levels of performance are being demanded, dielectric constants of 3.0 or lower are now required, and the development of films that use materials based on either Si systems or organic systems that contain no Si is being actively pursued. Furthermore, recently, research and development into lowering the dielectric constant by introducing vacancies (pores) into films has also become very active.
However, these types of low dielectric constant insulating films composed of porous materials tend to have properties that include low mechanical strength for the film itself and low plasma resistance. As a result, when these types of insulating films are subjected to a plasma treatment such as a plasma film deposition treatment, a plasma ashing treatment, or a plasma etching treatment conducted during Cu/Low-k wiring processing, in the case of a Si-based material, the organic groups such as methyl groups that are bonded to the Si—O backbone of siloxane linkages that constitutes the majority of the insulating film tend to be cleaved and eliminated. Further, in the case of an organic film, organic groups or organic bonds tend to be cleaved. It is known that a phenomenon in which the electrical properties deteriorate markedly, with the dielectric constant of the insulating film increasing significantly, accompanies this type of alteration in the film structure.
In terms of a more detailed mechanism of how this deterioration in the electrical properties of the semiconductor device occurs, it is thought that silanol groups formed by small quantities of moisture in the atmosphere bonding to the Si active sites generated by organic group cleavage resulting from the above plasma treatment, namely the damaged Si sites, cause the film to change from a hydrophobic state to a hydrophilic state, and as a result, further moisture adsorption occurs, thereby causing a deterioration in the electrical properties associated with Cu diffusion and an increase in the dielectric constant of the insulating film.
As a method of restoring, as far as possible, an insulating film that has been subjected to this type of deterioration to the state that existed prior to the plasma treatment, a method is disclosed in “Silicon Technology”, 2005, vol. 71, pp. 39 to 42 in which a porous siloxane-based insulating film that has been deteriorated by plasma treatment is subjected to a heat treatment at 400° C. in an atmosphere of a remedial agent composed of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS).
Furthermore, as another remedial method, a TA treatment method in which a liquid remedial agent is applied to an insulating film that has been deteriorated, and a heat treatment is then performed at approximately 350° C. has been proposed by Honeywell Inc., U.S.A.
However, in the first remedial method, there is a chance that the remedial agent used during the remedial treatment may remain on the copper wiring layer, resulting in an increase in the contact resistance of contact sections where the remedial agent covers the copper as a coating, and causing deterioration in the electrical properties.
Further, in the second method, an extra step of applying the liquid remedial agent is required, meaning an increase in the number of apparatus required for producing the device and an increase in the number of process steps, which is problematic in terms of mass production.